A combined mechanism mediated by lochons and phonons for cuprate superconductors

Abstract

We present a brief review of the combined pairing mechanism mediated by phonons and lochons (local charged bosons) for the high temperature superconducting materials (mainly cuprates). The phonon contribution (λ_p) being weak, the lochon part (λ_l) dominates to give higher critical temperatures (T_c). The combined mechanism along with the variation of λ_l with carrier concentration (x_c) gives the right variation of T_c and the oxygen isotope exponent on doping. The superconducting gap Δ(0) at T = 0, its ratio with T_c, the condensation energy, gap anisotropy, pseudogap, etc. are also discussed. With reasonable agreement with available experimental data, the combined mechanism emerges as a strong contender for an acceptable model for oxide superconducting materials.